The present invention relates to a disk array device using a combination of a plurality of physical disks to realize data redundancy and, more particularly, to a disk array device capable of dynamically reconfiguring logical disks.
Recently, disk array devices have been used for various information processing apparatuses. A disk array device is designed to realize high-speed access to data and high durability against failures by connecting a plurality of information storage media (physical disks) such as hard disks in parallel and synchronously controlling them as one storage unit.
In general, a disk array device has a plurality of physical disks. Since the processing speed of each physical disk is limited, the overall performance of the device is higher when accesses are distributed than when accesses concentrate on a specific physical disk. In degradation, in particular, since data generating operation is performed, if accesses concentrate on a degraded portion, the performance may greatly deteriorate. For this reason, it is preferable in terms of performance that accesses be distributed to physical disks as many as possible. That is, an excessive deterioration in performance can be prevented by distributing accesses to a plurality of physical disks instead of concentrating accesses to a specific logical disk.
In an information storage apparatus using such a disk array device, information is distributed and stored in a plurality of disks, and high reliability of data management is realized by using a parity disk. Assume that data cannot be read out from some disk of a plurality of physical disks required to construct one disk array device owing to a failure or the like. In this case, the information stored in the disk incapable of data read can be restored on the basis of the remaining disks constituting the disk array device.
Conventional techniques associated with such a disk array device are disclosed in Japanese Patent Laid-Open Nos. 03-103918, 04-370823, and 08-263226.
The disk array device disclosed in Japanese Patent Laid-Open No. 03-103918 uses a plurality of disk devices as one disk device to increase the data transfer rate between the memory and the disk devices.
In the disk array device disclosed in Japanese Patent Laid-Open No. 04-370823, the operation modes of the device are classified into a division mode in which the respective disk devices operate independently, an array mode in which the respective disk devices are combined into one logical device, and a mixed mode in which the above two modes are active. This disk array device allows arbitrary selection of an operation mode to offer some ranges of capacity per logical device and transfer rate, thereby improving the use efficiency in accordance with the use environment for a user.
In the disk array device disclosed in Japanese Patent Laid-Open No. 08-263226, a plurality of portable recording media are connected in parallel to logically construct one storage unit. This disk array device prevents unnecessary data from being restored owing to a cause other than a recording medium failure, e.g., temporary removal of a portable recording medium or a loss, and prevents redundant use of portable recording media, thereby improving reliability.
In a disk array device like those described above, since the configuration of a logical disk having a plurality of physical disks connected in parallel is basically fixed, when a physical disk is added afterward, the logical disk is reconfigured by formatting performed by an OS (Operating System) or the like. For this reason, even if a physical disk is added afterward, it is difficult to distribute disk accesses to the overall device including the existing physical disks and the added physical disk. Therefore, a satisfactory access distribution effect cannot be obtained.
In addition, in order to effectively distribute accesses to the added physical disk, the logical disk must be reconfigured after normal processing such as data write and read is stopped. This imposes great limitations on the utility of the device.